SAN FRANCISCO (CBS SF) – The 100,000 U.S. troops now stationed in Afghanistan should be trimmed to 10,000 to 25,000 within the next 18 months, Sen. Barbara Boxer said Friday.

“I am not suggesting that we walk away from Afghanistan tomorrow. Rather what I am recommending is a very different mission,” she said.

President Barack Obama has indicated U.S. forces will be in Afghanistan until at least 2014. Democrats have pushed for greater troop withdrawals as the surge winds down this summer.

Boxer, who serves on the Senate Foreign Relations Committee, said the diminished ranks of al Qaeda in Afghanistan and the continued presence of NATO forces would allow the U.S. to concentrate instead on targeted counterterrorism operations like the one that killed Osama bin Laden in May.

“The raid that killed Osama bin Laden was the result of months of sophisticated intelligence gathering and was carried out by dozens, not thousands, of extraordinary forces,” she said.

KCBS’ Tim Ryan Reports:

Boxer Calls For Major Afghanistan Troop Withdrawal During San Francisco Speech

In the vision Boxer outlined before an audience of the World Affairs Council in San Francisco on Friday, a slimmed down U.S. contingent would also continue to train Afghan security forces and provide security for coalition personnel.

“Ten thousand to 25,000 troops would be adequate to fulfill that kind of mission,” she said.

Boxer said the human costs of the longest war in American history had become too great and the U.S. roll there must evolve.

So far 177 U.S. service members have died in Afghanistan this year. Thirty-two coalition troops have died this month as the Taliban continues its spring offensive to regain ground lost during the winter.

Boxer also pointed to the tremendous financial cost of fighting in both Afghanistan and Iraq. She said ending the two wars could save the country $1 trillion over the 10 years.

(Copyright 2011 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services may have contributed to this report.)